In the prior art practice, the power absorbed by a human body, for example, by the head of the human body, has been estimated by constructing a head simulation phantom which simulates the configuration and the electromagnetic characteristics of the head of the human body and measuring the amount of power absorbed by the phantom.
A conventional example of the prior art will be described with reference to FIG. 1. A head simulation phantom 2 is constructed by forming a recess 12 configured to divide the head of the human body into two equal parts laterally in a top surface of a vessel 11 and filling the recess 12 with a liquid medium 10 which simulates the electromagnetic characteristics of the head. By way of example, the liquid medium for a 900 MHz solution comprises 56.5% of sucrose, 40.92% of deionized water, 1.48% of sodium chloride, 1.0% of hydroxyl cellulose and 0.1% of bactericide as disclosed in a literature IEC/PT62209, “Procedure to Determine the Specific Absorption Rate (SAR) for Hand-held Mobile Telephones” or the like. A radio transmitter 3 which represents a radio wave radiation source is secured to the bottom surface of the vessel 11 on the outside thereof at a location central of the vessel 11 or which corresponds to the ear of the head of the human body. An electromagnetic field probe 1 which detects an electric or a magnetic field is inserted into the liquid medium 10 and is scanned in a plane which opposes the radio transmitter 3. In this instance, the head simulation phantom 2 and the radio transmitter 3 are separately secured and only the electromagnetic field probe 1 is moved as indicated by arrows 8 for purpose of scan. A resulting detected value of the electromagnetic field probe 1 is squared, and the squared value is multiplied by a calibration facter to determine the absorbed power which occurs within the head simulation phantom 2. Broken lines 6, shown laterally offset, represent the locus of scan of the probe 1, and this corresponds to the measurement of absorbed power from the radio wave in a situation that the mobile telephone is located close to the ear of the head of the human body during the transmission and reception with the antenna (not shown) of the radio transmitter 3 extending in a direction through the casing of the radio transmitter 3 which runs substantially parallel to the bottom surface of the vessel 11.
The head simulation phantom 2 shown in FIG. 1 is filled with the liquid medium 10, and is inconvenient in its handling. Since the probe 1 is moved within the liquid medium 10 for purpose of scan and measurement, the liquid medium 10 remains open to the air, and there arises a problem that the liquid medium 10 may be evaporated to cause an aging effect of the electromagnetic characteristics thereof.
Another example of the prior art will be described with reference to FIG. 2. A head simulation phantom 2 which simulates the configuration and the electromagnetic characteristics of the head of the human body is constructed, and an electromagnetic field probe 1 is inserted into an opening 21 formed in the phantom 2. The electromagnetic field probe 1 is located close to the ear of the head simulation phantom 2, while a radio transmitter 3 which represents a radio wave radiation source is positioned on the external surface of the head simulation phantom 2 close to the ear. The transmitter 3 is moved vertically and back-and-forth, as indicated by arrows 8, for purpose of two-dimensional scan while deriving a detected value from the electromagnetic probe 1, and multiplying a calibration factor to the square of the detected value to determine the absorbed power. The locus of scan for this case is illustrated by broken line 6, shown laterally offset. It is assumed in FIG. 2 that a mobile telephone is used as the radio transmitter 3 with an antenna extended from the telephone case to simulate the manner of use of a mobile telephone.
The phantom 2 shown in FIG. 2 simulates the head of the human body by a spherical solid dielectric 10′ or by a liquid dielectric (liquid medium) 10 which fills the interior of a spherical vessel. The solid dielectric 10′ has a dielectric constant εr′=52 and a dielectric loss tan δ=55% (at 900 Mhz), for example, and comprises 57% of polyvinylidene fluoride, 10% of ceramic powder and 33% (volume %) of graphite powder, as disclosed in a literature by H. Tamura, Y. Ishikawa, T. Kobayashi and T. Nojima “A Dry Phantom Material Composed of Ceramic and Graphite Powder,” IEEE Trans. Electromagn. Compat., Vol. 39, No. 2, pp 132–137, May 1997 or the like.
Assuming that the head phantom2 is formed with a size simulating the head of the human body, or with a sphere having a diameter of 200 mm, it contains a volume of 4×π×{(200/2)mm}3/3. The dielectric which simulates the electromagnetic characteristics of the head of the human body has a density which is equal to about 0.002 g/mm3 for the solid dielectric 10′ and which is equal to about 0.001 g/m3 for the liquid dielectric (liquid medium). Accordingly, the head simulation phantom 2 has a weight which is equal to the volume 4×π×{(200/2)mm}3/3 multiplied by the density 0.002 g/mm3 or 8400 g for the solid dielectric 10′. Since the liquid dielectric 10 has a density which is nearly one-half that of the solid dielectric 10′, the phantom will have a weight which is nearly one-half that of the solid dielectric 10′ phantom. Thus, a conventional head simulation phantom 2 has a weight which is as high as 4200 g or 8400 g, and presented an inconvenience in its handling and transportation.
The purpose of measuring the absorbed power is to know how much of a radio wave is absorbed by the human body during the use of a mobile telephone or a transceiver, and the measurement takes place in a so-called near field in which a distance from a radio wave radiation source to the phantom 2 is normally very small. As a consequence, there is a great influence that the reproducibility of positional relationship between the radio transmitter 3, the head simulation phantom 2 and the electromagnetic field probe 1 has upon the reproducibility of results of measurement. In other words, if there is a relatively small shift in the relationship, there occurs a change in the reflection characteristic of the phantom 2, producing a change in the distribution of the radiated electromagnetic field. If the radio transmitter 3 is held by the hand 4′ of a measuring personnel as indicated in FIG. 3, it is difficult to maintain a correct position of the transmitter relative to the phantom 2, and a good reproducibility of measured values cannot be guaranteed. There also occur influences that the radio wave radiated from the radio transmitter 3 is absorbed by the hand 4′ of the measuring person and that the current distribution on the antenna 5 of the radio transmitter 3 may be changed due to the hand 4′ of the measuring personnel. Where the radio transmitter has a bulky volume or heavy, it may be difficult to conduct a spatial scan of the radio transmitter 3 relative to the phantom 2 by hand 4′.
Conversely, if the radio transmitter 3 is fixed while the absorbed power measuring assembly 7 comprising the head simulation phantom 2 and the electromagnetic field probe 1 scans through a two-dimensional movement relative to the radio transmitter 3, it is a troublesome operation to perform the measurement by manually moving and scanning the absorbed power measuring assembly 7 when the head simulation phantom 2 has a weight which is as high as 4200 g or 8400 g as described above.
It is an object of the present invention to provide an apparatus for measuring absorbed power which permits a scan through a relative movement between an absorbed power measuring assembly comprising a simulation phantom and an electromagnetic field probe and a radio transmitter to be performed in a relatively simple manner.